Method for transmitting multiple streams in wireless broadcast networks

ABSTRACT

Accordingly, a method and apparatus are provided to convert received content into a first stream and a second stream, to transmit said first stream using a first tone and to transmit said second stream using an orthogonal scheme. A layering scheme is used to transmit the base stream covering a smaller area and an enhanced stream is used to cover a large utilizing orthogonal scheme.

CLAIM OF PRIORITY UNDER 35 U.S.C. §119

The present Application for Patent claims priority to ProvisionalApplication No. 60/540,310 entitled “HIERARCHICAL CODING IN AMULTI-FREQUENCY BROADCAST NETWORK” filed Jan. 28, 2004, and assigned tothe assignee hereof and hereby expressly incorporated by referenceherein.

FIELD OF INVENTION

The present invention relates generally to a broadcast system, moreparticularly, to a broadcast of content from transmitters from differentgeographical areas.

BACKGROUND

Wireless communication systems are widely deployed to provide varioustypes of communication content such as voice, data, and so on. Thesesystems may be multiple-access systems capable of supportingcommunication with multiple users by sharing the available systemresources (e.g., bandwidth and transmit power). Examples of suchmultiple-access systems include code division multiple access (CDMA)systems, time division multiple access (TDMA) systems, frequencydivision multiple access (FDMA) systems, and orthogonal frequencydivision multiple access (OFDMA) systems.

The wireless communication system further employs a broadcast system,wherein portion of the forward link resources are dedicated forbroadcasting content. In the broadcast system, all the recipientsprocess data received on the dedicated channel on the forward link(i.e., frequency tones that make up a shared channel), as if theinformation was targeted for the recipient. A typical broadcast systemdoes not require any acknowledgement from the recipients regarding thereception of data. However, operators of the system, generally configurethe AP (or access points) to use low data rate (e.g., repeat thetransmission data packets that make up the content) and at high power inorder to insure that all the mobile stations within the base station'scoverage area receive the content, including any mobile stations thatare far from the base station. However, low data rates are generallyneeded only for mobile stations that operate far from the currentlyservicing base station. Thus, all the mobile stations that operate nearthe base station cannot enjoy higher data rates.

Therefore, a method is needed to manage the broadcast resources toreduce the coverage hole.

BRIEF SUMMARY OF THE INVENTION

Accordingly, a method and apparatus are provided to convert receivedcontent into a first stream and a second stream, to transmit said firststream using a first set of tones and to transmit said second streamusing an orthogonal scheme._A more complete appreciation of all theadvantages and scope of the invention can be obtained from theaccompanying drawings, the description and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The features, nature, and advantages of the present invention willbecome more apparent from the detailed description set forth below whentaken in conjunction with the drawings in which like referencecharacters identify correspondingly throughout and wherein:

FIG. 1 shows a diagram of a wireless multiple-access communicationsystem;

FIG. 2 a block diagram of a communication system;

FIG. 3 shows an illustration of exemplary frame of a communicationsystem; and

FIG. 4 illustrates a process for broadcasting content using two streams.

DETAILED DESCRIPTION

The word “exemplary” is used herein to mean “serving as an example,instance, or illustration.” Any embodiment or design described herein as“exemplary” is not necessarily to be construed as preferred oradvantageous over other embodiments or designs. The word “listening” isused herein to mean that a terminal is receiving and processing datareceived on a given channel.

FIG. 1 shows a diagram of a wireless multiple-access communicationsystem 100 that employs multi-carrier modulation. System 100 as shownincludes access points, for example 102 a and 102 b that communicatewith a number of access terminals 130 a-130 b. For simplicity, only twoaccess points 102 a and 102 b and only two access terminals 130 a-130 bare shown in FIG. 1. For purpose of discussion, when referring to asingle access terminal (AT) 130 x is used and when referring to a singleaccess point (AP) 102 x will be used. Components of access terminal 130x and access point 102 x are described in FIG. 2, below.

For illustration, AP 102 a services service area 1 and AP 102 b servicesservice area 2. The AP 102 a has service coverage defined by 106 havinga radius vector 120 and the AP 102 b has service coverage defined by 108having a radius vector 122. As discussed below, area 106 and 108 areserviced using the base streams for broadcast system. Note that 106 and108 assumes that interference does not exit. Once the APs 102 a and 102b are placed adjacent to each other as shown in FIG. 1, the service areais reduced and defined as coverage hole 116. Also, AP 102 a and 102 bfurther defines a service area 110 and 112, respectively, and areaserviced using a layered scheme (e.g. use of both enhanced stream andbase stream), discussed below.

As discussed above, a coverage hole 116 is shown for illustrating thearea where signals from AP 102 a and AP 102 b interfere with each other.For illustration, the coverage hole boundary 114 is shown which definesthe coverage hole 106. As shown in FIG. 1, the AT 130 b, operatingwithin coverage hole boundary 114 would not be able to receive thecontent.

An access point 102 x, is an electronic device configured to communicatewith one or more user access terminals and may also be referred to as abase station, base terminal, fixed terminal, a fixed station, basestation controller, a controller, transmitter or some other terminology.The access point, base terminal, and base station are interchangeablyused in the description below. The access point 102 x may be a generalpurpose computer, a standard laptop, a fixed terminal, an electronicdevice configured to transmit, receive and process data according to airinterface methods defined by an OFDMA, CDMA, GSM, WCDMA, etc., or anelectronic module comprising one or more computer chips controlled by acontroller or a processor for transmitting, receiving and processingdata according to air interface methods defined by an OFDMA, CDMA, GSM,WCDMA, etc.

An AT 130 x, is an electronic device configured to communicate with theaccess point via a communication link. The AT 130 x may also be referredto as a terminal, a user terminal, a remote station, a mobile station, awireless communication device, recipient terminal, or some otherterminology. The AT 130 x, mobile terminal, user terminal, terminal areinterchangeably used in the description below. Each AT 130 x maycommunicate with one or multiple access points on the downlink and/oruplink at any given moment. The downlink (i.e., forward link) refers totransmission from the access point to the AT 130 x, and the uplink(i.e., reverse link) refers to transmission from the AT 130 x to theaccess point. The AT 130 x may be any standard laptop, personalelectronic organizer or assistant, a mobile phone, cellular phone, anelectronic device configured to transmit, receive and process dataaccording to air interface methods defined by an OFDMA, CDMA, GSM,WCDMA, etc. system, or an electronic module comprising one or morecomputer chips controlled by a controller or a processor fortransmitting, receiving and processing data according to air interfacemethods defined by an OFDMA, CDMA, GSM, WCDMA, etc. system.

A system controller 140 couples to the access points and may furthercouple to other systems/networks (e.g., a packet data network). Systemcontroller 140 provides coordination and control for the access pointscoupled to it. Via the access points, system controller 140 furthercontrols the routing of data among the terminals, and between theterminals and other users coupled to the other systems/networks. Thesystem controller 140 may be used to update the transmit information forthe base and enhanced streams.

FIG. 2 shows a block diagram of an embodiment of two access points 102 xand 102 y and a AT 130 x in multiple-access multi-carrier communicationsystem 200. At access point 102 x, a transmit (TX) data processor 214receives content data from a data source 212 and signaling and otherinformation from a controller 220 and a scheduler 230. These varioustypes of data may be sent on different transport or broadcast channels.TX data processor 214 encodes and modulates the received data usingmulti-carrier modulation (e.g., OFDM) to provide modulated data (e.g.,OFDM symbols). For example, the controller 220 converts the content intotwo data streams, a base stream and an enhanced stream. The controller220 modulates the stream based on pre-determined scheme. A transmitterunit (TMTR) 216 then processes the modulated data to generate a downlinkmodulated signal that is then transmitted from an antenna 218.

The terminal 130 x receives the modulated signal via an antenna 252 andprovides to a receiver unit (RCVR) 254. Receiver unit 254 processes anddigitizes the received signal to provide samples. A received (RX) dataprocessor 256 then demodulates and decodes the samples to providedecoded data, which may include recovered traffic data, messages,signaling, and so on. The traffic data may be provided to a data sink258, and the carrier assignment sent for the terminal are provided to acontroller 260.

Controller 260 processes the received data stream based on informationprovided by the AP 102 x during registration process. For each activeterminal 130, a TX data processor 274 receives traffic data from a datasource 272 and signaling and other information from controller 260. Thevarious types of data are coded and modulated by TX data processor 274using the assigned carriers and further processed by a transmitter unit276 to generate an uplink modulated signal that is then transmitted fromantenna 252.

At access point 102 x, the transmitted and modulated signals from theterminals are received by antenna 218, processed by a receiver unit 232,and demodulated and decoded by an RX data processor 234. Receiver unit232 may estimate the received signal quality (e.g., the receivedsignal-to-noise ratio (SNR)) for each terminal and provide thisinformation to controller 220. Controller 220 may then derive the PCcommands for each terminal such that the received signal quality for theterminal is maintained within an acceptable range. RX data processor 234provides the recovered feedback information (e.g., the required transmitpower) for each terminal to controller 220 and scheduler 230.

For clarity, techniques described herein are described in reference toan OFDMA system that utilizes orthogonal frequency division multiplexing(OFDM). In this system, for forward link, several frames are used totransmit signaling information, content data, etc. FIG. 3 illustrates aframe 302 used in the OFDMA system. The frame is defined by frequencyand time. With each frame, based on available resources, multiple tones,for example 304, 306 and 308, are defined for transmitting data. A tonecomprises frequency value for duration of time. The frequency value isdetermined by the operator based on the available resources. Asdiscussed in detail below, for transmitting streams using layeredmodulation, tone 304 may be used, wherein two streams may be layered,for transmitting the streams. Using the orthogonal scheme, wherein thetone 306 used by a first AP 102 x and tone 308 is used by a second AP102 x. This will allow the AT 130 b operating within the coverage holeto discard information received on tone 306 or 308, depending on servicearea associated with AT 130 b. For example, if AT 130 b is associatedwith service area 2 (serviced by second AP 102 x), then AT 130 b willignore tone 306 transmitted by first AP 102 x.

According to an embodiment, a layered modulation (also referred to aslayered scheme) in a broadcast system is employed. Layered modulationconsists of transmitting multiple streams together, with each streamtargeted towards a subset of users with a certain minimum channelquality. Users with better channel quality (user near the AP 102 x) willbe able to decode more than one stream and hence achieve higher datarates. Since users well within the service area are likely to havebetter channels, the goal of layered modulation is to provide betterthroughput in the interior of the channel. Combining this with thetrade-off provided with re-use, the basic idea behind our proposal canbe summarized as: use different re-use techniques for different streamsin a system with layered modulation.

For simplicity, the OFDM broadcast system is used for illustration. Notethat the methods described herein may be employed using any other systemthat provides broadcast capabilities and orthogonalization capabilitiesacross transmitters. Furthermore, only one AP 102 x is used for aservice area and two service areas used for illustration purposes, asshown in FIG. 1 above. Also, the broadcast is done using OFDM and re-useis achieved by allocating disjoint sets of tones to each AP 102 x. Thenumber of tones in each set is equal. It is assumed that the signal fromeach AP 102 x goes through an additive white Guassian noise (AWGN)channel and the layered modulation comprises of sending two streams, abase stream targeted towards all users in the service areas and anenhancement stream targeted towards users with better signal-to-noiseratio (SNR).

Assume the OFDM scheme comprises of using 2N data tones. These 2N tonesare divided into two disjoint sets, N_(b, 1)and N_(b, 2),each with N tones. At the first AP 102 x, the transmitted symbols at thedifferent tones are given by $\begin{matrix}{{{{s_{1}(k)} = {{\sqrt{P_{b,1}}{x_{b,1}(k)}} + {\sqrt{P_{e,1}}{x_{e,1}(k)}}}},}\quad} & {k \in N_{b,1}} \\{{= {\sqrt{P_{e,1}}{x_{e,1}(k)}}},} & {k \in N_{b,2}}\end{matrix}$where x_(b, 1)and x_(e, 1)are the symbols from the base and enhancement streams (i.e., Layeredscheme), with powers P_(b, 1)and P_(e, 1)respectively. In other words, both base and enhancement streams are senton N_(b, 1)tones, while only the enhancement stream is sent on the remainingN_(b,2) tones. Note that the power allocated to the base stream istypically larger than that for the enhancement stream must satisfy theoverall constraint:NP _(b,1)2NP _(e,1)=const.  Equation 1The symbol from the second service area can be written in a similarmanner, with the base streams transmitted on the N_(b,2) tones and theenhancement stream transmitted on all tones.

Consider now the received symbol at the tone k at any point in Servicearea 1.y(k)=s ₁(k)+βs ₂(k)+n(k)

-   -   where β represents the strength of the signal from the second AP        102 x relative to that from the first AP 102 x, n(k) is Guassian        noise with variation σ², and the parameters β & σ² depend on the        location in the coverage area. Thus, for the set of tones in        N_(b,1), the receiver sees interference from the enhancement        streams from both service areas, but none from the base stream        2. The decoding of the base stream treats the two enhancement        streams as additive interference. Once the base stream is        decoded, it is subtracted from the received symbols, so that the        enhancement stream 1, sees interference from the enhancement        stream 2 on all tones. In addition, for the tones in N_(b,2),        interference is seen from base stream 2 as well. The decoding of        the enhancement stream treats these as additive interference. It        may seem that interference from base stream 2 would severely        degrade performance of the enhancement stream 1, but the key is        that enhancement stream 1 is expected to be decoded only in the        interior points and hence base stream 2 would be significantly        attenuated.

We can characterize the performance of the above scheme in terms oftheoretical spectral efficiency based on the Shannon capacity of andAWGN channel. The rate for the base stream is determined by worst casewhere signal-to-interference-plus-noise (SINR) in Service area 1, whereSINR includes interference from the two enhancement streams. Let Pdenote such a point at the edge of coverage, with noise variance σ_(p) ²and interference attenuation β_(p). The spectral efficiency for the basestream is given by $\begin{matrix}{R_{b,1} = {\frac{1}{2}\log\quad\left( {1 + \frac{P_{b,1}}{\sigma_{p}^{2} + P_{e,1} + {\beta_{p}P_{e,2}}}} \right)\quad{bps}\text{/}{Hz}}} & {{Equation}\quad 2}\end{matrix}$where the factor of ½ arises because we are using only half the tones.

Similarly, the rate for the enhancement stream is governed by the worstcase SINR in a smaller coverage area, where the SINR includes basestream 2 and enhancement stream 2. Let σ_(q) ² and β_(q) be the noisevariance for a point at the edge of coverage for the enhancement stream.Note that, since this coverage area is smaller than that for the basestream, we have β_(q)<β_(p) and σ_(q) ²<σ_(p) ². Hence the overallinterference is lesser at point q, and the base stream is decodable atq. The rate of the enhanced stream at point q is given by$\begin{matrix}{R_{e,1} = {{\frac{1}{2}\log\quad\left( {1 + \frac{P_{e,1}}{\sigma_{q}^{2} + {\beta_{q}P_{e,2}}}} \right)} + \quad{\frac{1}{2}\log\quad\left( {1 + \frac{P_{e,1}}{\sigma_{q}^{2} + {\beta_{q}\left( {P_{e2} + P_{b2}} \right)}}} \right)\quad{bps}\text{/}{Hz}}}} & {{Equation}\quad 3}\end{matrix}$For typical interference conditions, it can be shown that the aboverates for the base and enhancement streams are larger than those with noreuse for the base (i.e. all 2N tones used for both base andenhancement) as well as those with a reuse factor of two (i.e. only Ntones used for base and enhancement at each transmitter).

Generally, the service provider maps out the physical location of theAP. Thereafter, several AP are identified as likely to have the coveragehole, discussed above. For these AP, the tones used for carrying out thedisclosed implementation may be pre-selected, modified over the air, ordynamically controlled the access controller.

FIG. 4 illustrates a process 400, for broadcasting content using twostreams. The AP 102 x is configured to execute steps of the process 400by utilizing at least one of various components described in FIG. 2 forexample, the controller 220, the scheduler 230, the memory 222, the TXdata processor 214, RX data processor 234, etc. In an embodiment, AP 102x is pre-selected to utilize the techniques discussed above. At step402, AP 102 x converts the content into two streams, a first stream(i.e., enhanced stream) and a second stream (i.e. base stream). Thestreams may be series of data packet of the content. The enhanced streamis modulated to provided additional data rate in a smaller coverage areathan the base stream. At step 404, the AP 102 x transmits both streamsusing the layered scheme, discussed above. At step 406, the AP 102 x,uses a pre-selected tone to transmit the base stream. The frequency ofpre-selected tone is orthogonal to the frequency of tone used by one ormore of the adjacent AP 102 x. In an alternate embodiment the samefrequency may used for transmitting the base stream, wherein the time(symbol) of transmission is orthogonal to the adjacent AP 102 x.

The techniques described herein may be implemented by various means. Forexample, these techniques may be implemented in hardware, software, or acombination thereof. For a hardware implementation, the processing units(e.g., controllers 220 and 270, TX and RX processors 214 and 234, and soon) for these techniques may be implemented within one or moreapplication specific integrated circuits (ASICs), digital signalprocessors (DSPs), digital signal processing devices (DSPDs),programmable logic devices (PLDs), field programmable gate arrays(FPGAs), processors, controllers, micro-controllers, microprocessors,other electronic units designed to perform the functions describedherein, or a combination thereof.

For a software implementation, the techniques described herein may beimplemented with modules (e.g., procedures, functions, and so on) thatperform the functions described herein. The software codes may be storedin memory units (e.g., memory 222 in FIG. 2) and executed by processors(e.g., controllers 220). The memory unit may be implemented within theprocessor or external to the processor, in which case it can becommunicatively coupled to the processor via various means as is knownin the art.

Headings are included herein for reference and to aid in locatingcertain sections. These headings are not intended to limit the scope ofthe concepts described therein under, and these concepts may haveapplicability in other sections throughout the entire specification.

The previous description of the disclosed embodiments is provided toenable any person skilled in the art to make or use the presentinvention. Various modifications to these embodiments will be readilyapparent to those skilled in the art, and the generic principles definedherein may be applied to other embodiments without departing from thespirit or scope of the invention. Thus, the present invention is notintended to be limited to the embodiments shown herein but is to beaccorded the widest scope consistent with the principles and novelfeatures disclosed herein.

1. A method of broadcasting a content in a wireless communicationsystem, said method comprising acts of: converting the content into afirst stream and a second stream; transmitting said first stream using afirst tone; and transmitting said second stream using an orthogonalscheme.
 2. The method as claimed in claim 1, wherein said acttransmitting said second stream using an orthogonal scheme furthercomprises act of utilizing a second tone that is orthogonal to a toneused by adjacent access point.
 3. The method as claimed in claim 1,further comprising an act of transmitting said second stream using saidfirst tone along with said first stream.
 4. The method as claimed inclaim 1, wherein said act of transmitting said first stream comprisesact of transmitting said first stream at a first data rate; and said actof transmitting said second stream comprises act of transmitting saidfirst stream at a second data rate.
 5. The method as claimed in claim 3,wherein said act of transmitting said first stream comprises act oftransmitting said first stream at a first data rate; and said act oftransmitting said second stream comprises act of transmitting said firststream at a second data rate that is lower that said first data rate. 6.The method as claimed in claim 1, further comprising an act oftransmitting said second stream comprises act of using power level forsecond stream that is different than power level used for first stream.7. The method as claimed in claim 3, further comprising an act oflayering said first stream and said second stream on said first tone. 8.The method as claimed in claim 1, wherein the said of transmittingfurther comprising act of transmitting in accordance with a CodeDivision Multiplex Access (CDMA) scheme.
 9. The method as claimed inclaim 1, wherein the said of transmitting further comprising act oftransmitting in accordance with an Orthogonal Frequency DivisionMultiplex (OFDM) scheme.
 10. The method as claimed in claim 1, whereinsaid act of transmitting further comprising act of transmitting inaccordance with an Orthogonal Frequency Division Multiple Access (OFDMA)scheme.
 11. An apparatus for broadcasting a content in a wirelesscommunication system, said apparatus comprising: means for convertingthe content into a first stream and a second stream; means fortransmitting said first stream using a first tone; and means fortransmitting said second stream using an orthogonal scheme.
 12. Theapparatus as claimed in claim 11, wherein said means for transmittingsaid second stream comprises means for utilizing second tone that isorthogonal to a tone used by adjacent access point.
 13. The apparatus asclaimed in claim 11, further comprising means for transmitting saidsecond stream using said first tone along with said first stream. 14.The apparatus as claimed in claim 11, wherein said means fortransmitting said first stream comprises means for transmitting saidfirst stream at a first data rate; and said means for transmitting saidsecond stream comprises means for transmitting said first stream at asecond data rate.
 15. The apparatus as claimed in claim 13, wherein saidmeans for transmitting said first stream comprises means fortransmitting said first stream at a first data rate; and said means fortransmitting said second stream comprises means for transmitting saidfirst stream at a second data rate that is lower that said first datarate.
 16. The apparatus as claimed in claim 11, further comprising meansfor using power level for transmitting said second stream that isdifferent than power level used for first stream.
 17. The apparatus asclaimed in claim 13, further comprising an means for layering said firststream and said second stream on said first tone.
 18. The apparatus asclaimed in claim 11, wherein the said of transmitting further comprisingmeans for transmitting in accordance with a Code Division MultiplexAccess (CDMA) scheme.
 19. The apparatus as claimed in claim 11, whereinthe said of transmitting further comprising means for transmitting inaccordance with an Orthogonal Frequency Division Multiplex (OFDM)scheme.
 20. The apparatus as claimed in claim 11, wherein said means fortransmitting further comprising means for transmitting in accordancewith an Orthogonal Frequency Division Multiple Access (OFDMA) scheme.21. In a wireless communication system, an apparatus comprising: anelectronic device, said electronic device configured to convert receivedcontent into a first stream and a second stream, configured to transmitsaid first stream using a first tone and configured to transmit saidsecond stream using an orthogonal scheme.
 22. The apparatus as claimedin claim 21, wherein said electronic device is configured to utilizesaid second tone that is orthogonal to a tone used by adjacent accesspoint.
 23. The apparatus as claimed in claim 21, said electronic devicefurther configured to transmit said second stream using said first tonealong with said first stream.
 24. The apparatus as claimed in claim 21,wherein said electronic device is further configured to transmit saidfirst stream at a first data rate; and said electronic device is furtherconfigured to transmit said first stream at a second data rate.
 25. Theapparatus as claimed in claim 23, wherein said electronic device isfurther configured to transmit said first stream at a first data rate;and said electronic device is further configured to transmit said firststream at a second data rate.
 26. The apparatus as claimed in claim 21,said electronic device is further configured to use power level that isdifferent than power level used for first stream.
 27. The apparatus asclaimed in claim 23, said electronic device is further configured tolayer said first stream and said second stream on said first tone.
 28. Amachine-readable medium comprising instructions which, when executed bya machine, cause the machine to perform operations including: convertingthe content into a first stream and a second stream; transmitting saidfirst stream using a first tone; and transmitting said second streamusing an orthogonal scheme.
 29. The machine-readable medium as claimedin claim 28, wherein said machine readable instruction to causetransmitting said second stream using an orthogonal scheme furthercomprises instruction for utilizing a second tone that is orthogonal toa tone used by adjacent access point.
 30. A broadcast system, saidsystem comprising: a first access point and an adjacent access point;said first access point configured to convert the content into a firststream and a second stream; transmit said first stream using a firsttone, and transmit said second stream using second tone.
 31. Thebroadcast system as claimed in claim 30, wherein said second tone usedby first access point is orthogonal to said a tone used by said adjacentaccess point.